The present invention relates generally to a n-port junction device for processing modulated digital RF signals, a direct receiver comprising such a n-port junction device, a mobile telecommunications device comprising such a direct receiver, a method for calibrating a n-port junction device and a method for processing modulated digital RF signals.
A six-port receiver is known acting in the direct conversion manner and allowing conversion from mm-wave range and microwave range directly to the base band. At the same time a classic I/Q-demodulation chip (digital or analog) can be avoided. By using suitable calibration procedures the influences of the non-ideal passive RF-components including manufacturing tolerances can be minimized. The six-port receiver detects the relative phase and relative magnitude of two incoming RF-signals. The circuitry of the six-port receiver is realized using only passive components in combination with diodes for the detection of the relative phase and the relative magnitude of the RF-signals. An important feature of six-port receivers is that fabrication tolerances can be calibrated, which inherently allows low-cost production.
In Bossisio, Wu xe2x80x9cA six-port direct digital millimeter wave receiverxe2x80x9d, Digest of 1994 IEEE MTT Symposium, vol. 3, page 1659-1662, San Diego, May 1994, a structure for a six-port receiver is proposed.
The six-port technique has been known for its ability to accurately measure the scattering parameters, both amplitude and phase, of microwave networks. Instead of using heterodyne receivers a six-port receiver accomplishes direct measurements at microwave and mm-wave frequencies by extracting power levels at least three and particularly four of the 6 ports. The imperfections of the hardware can be readily eliminated by an appropriate calibration procedure. Very accurate measurements can be made in a large dynamic range and wide frequency range. Six-port junction receivers consist of passive microwave components such as directional couplers and power dividers as well as diode detectors. The circuit can be easily integrated as MHMIC or MMIC. The known receiver performs direct phase/amplitude demodulation at microwave and mm-wave frequencies.
By performing a calibration procedure the hardware imperfections such as phase error of the bridges, imbalance of the power detectors, etc. can be readily eliminated. This significantly eases the requirement of the hardware implementation and enables the six-port receiver to operate over a wide band up to mm-wave frequencies.
According to the above cited document of Bossisio et. al. a six-port receiver concept with power dividers and 90 degrees hybrid circuits realized in distributed technology is used. The application of that known structure lies mainly in the frequency bands above 10 GHz, however, it suffers from an insufficient band width of the operation due to the inherently frequency selective nature of the 90 degrees hybrid circuits.
From D. Maurin, Y. Xu, B.Huyart, K. Wu, M. Cuhaci, R. Bossisio xe2x80x9cCPW Millimeter-Wave Six-Port Reflectometers using MHMIC and MMIC technologiesxe2x80x9d, European Microwave Conference 1994, pp.911-915, a wide-band topology for reflectometer used is known which is based on a distributing element approach featuring coplanar wave guide applications in the frequency range from 11 to 25 GHz.
From V. Bilik, et al. xe2x80x9cA new extremely wideband lumped six-port reflectometerxe2x80x9dEuropean Microwave Conference 1991, pp. 1473-1477 and the idea of using Wheatstone Bridges and resistive structures for reflectometer applications is known.
From j:Li, G.Bossisio, K. Wu, xe2x80x9cDual tone Calibration of Six-Port Junction and its application to the six-port direct digital receiverxe2x80x9d, IEEE Transactions on Microwave Theory and Techniques, vol. 40, January 1996 a six-port reflectometer topology based on four 3 dB hybrid circuits, power dividers and attenuators is known.
From U.S. Pat. No. 5.498,969 an asymmetrical topology for a reflectometer structure featuring matched detectors and one unmatched detector is known.
From U.S. Pat. No. 4,521,728 with the title xe2x80x9cMethod and six-port network for use in determining complex reflection coefficients of microwave networksxe2x80x9d a reflectometer six-port topology is known comprising two different quadrate hybrids, phase shifter, two power dividers and one directional coupler for which the realization by a microstrip line technology is disclosed.
From EP-A-0 805 561 a method for implementing a direct conversion receiver with a six-port junction is known. According to this known technique, modulated transmitted modulation is received by a direct conversion receiver which comprises a six-port junction. The demodulation is carried out analogically.
From EP-A-0 841 756 a correlator circuit for a six-port receiver is known. In this correlator circuit the received signal is summed up with a local oscillator signal at various phase angles, wherein the phase rotation between the local oscillator and RF signals is carried out separately from the summing of the correlator outputs.
In view of the above prior art, it is the object of the present invention to provide for a technique on the basis of an improved structure of a n-port junction device. n thereby is an integer value larger than 3. Therefore the present invention relates e.g. to a four-port, five-port and six-port junction devices as well as to devices comprising such n-port junction devices.
According to the present invention therefore a n-port junction device for processing modulated digital RF signals is provided, wherein n is an integer value larger than 3. The n-port junction device comprises two RF input ports. According to the present invention two passive signal-combining means are connected to each other. Respectively one of the passive signal-combining means is connected to one of the RF inputs and is furthermore connected by means of at least one output port to a power sensor, such that at least two power sensors are comprised in the n-port junction device.
The two passive signal-combining means can be connected with each other by means of a phase shifting element.
One of the RF input ports can be supplied to the RF signal originating from a local oscillator.
The passive signal-combining means can comprise a microstripline network. The passive signal-combining means can alternatively comprise a coplanar waveguide network.
The resistive network can comprise a microstrip ring.
The resistive network can comprise a circular microstrip patch.
The n-port junction device can be e.g. a four-port junction device (n=4) comprising two passive signal-combining means implemented as three-port junction devices respectively connected to one power sensor. Therefore in the case of four-port junction devices the three-port junction devices comprise one port being fed with the received RF signal, one port is respectively connected to the other one of the three-port junction devices and the third port is connected to a power sensor.
In the case of a four-port junction device at least one of the RF input ports has a RF switch.
The n-port junction device can be a five-port junction device (n=5) comprising two passive signal-combining means, wherein the first passive signal-combining means is implemented as a four-port junction device connected at two output ports to two power sensors and the second one of the passive signal-combining means is a three-port junction device connected to one power sensor.
The n-port junction device can be a six-port junction device (n=6) comprising two passive signal-combining means implemented as two four-port junction devices, wherein each of the four-port junction devices is connected to two power sensors.
According to the present invention furthermore a direct receiver comprising a n-port junction device as set forth above as well as a mobile telecommunications device comprising such a direct receiver is provided.
The invention furthermore relates to a method for calibrating a n-port junction device as set forth above wherein a predefined calibration signal is supplied to one of the RF input ports of the n-port junction device.
According to the present invention a method for processing modulated digital RF signals is provided. Thereby two input ports of a n-port junction device are respectively supplied with one RF signal, n being an integer larger than 3, the n-port junction device comprising two passive signal-combining means connected to each other and respectively one of the passive signal-combining means is connected to one of the two input ports of the n-port junction device. At least one output signal respectively from each of the passive signal-combining means is supplied to a power sensor.
The method can furthermore comprise the step of I/Q demodulating output signals of the power sensors, wherein the I/Q demodulation is effected by an analog processing.
Additionally to the output signals of the power sensors at least adjustable DC voltage can be used in the analog processing.